Heavy AD people have 
for mana regen.
Mages have 
and a lot more.
Tanks have no mana regen item. So I was thinking of a backwards essence reaver.
+500 hp +300 mana Passive: 2%-8% of damage taken is converted into mana.
Something like that. But mana heavy tanks need some sustain in that kind of way.
Cindikle2 votesNot really needed. They generally get flat mana to last longer rather than recover. You shouldn't be spamming spells for poke and such anyway since their worth is minimal compared to someone who built damage.
There's a reason Karthus, Kassadin and Swain are more likely to build flat mana. They can burn though mana too fast for recovery to really matter. An extra 400 mana will do them more good than an extra 50% regen.
Dangerous Man1 votesBut It isn't OP or broken, but useful, so why not add it?
Cindikle1 votesThe smallest change could easily offset the balance in the game.
Why put the risk for such a small change?
There's also Ryze. He's part of the reason Banshee's Vail no longer gives mana.
disregardable1 votesSo Swain can kill you forever! Yay tank meta!
Gym Leader Yaki1 votesThey have 
or 
It's not regen, but it's something.
Dangerous Man1 votesI just want something with decent regen AND HP at the same time.
Zarxis1 votesChalice of Harmony and its upgrades are also usable by tanks. They both provide MR and CDR, which are valuable tank stats. Both Catalyst upgrades provide survivability and sustain (up to level 18). Jungle tanks get mana regeneration from jungle items and blue buff.